The present invention relates to a pump adapted to provide a variable volumetric delivery which can be freely adjusted and, more particularly, to such a pump having reduced fluid resistance to impeller rotation and having a cover for adjusting the effective length of the impeller blades.
A conventional pump for a water-cooled engine is so designed that the maximum volume to be delivered from the pump matches a full load operational range in which the maximum amount of heat is emitted from the engine. Since the volume of water delivered from the pump is in proportion to the number of revolutions of the pump, a volumetric excess of water recirculates, resulting in a waste of energy.
A number of proposals have been advanced for curbing such waste. One such approach uses a variable speed motor to drive the water pump, whereby the number of pump revolutions is varied in accordance with the existent operational state of the engine to adjust the volume of water delivered from the pump. This approach, however, has not been commercially utilized because of the expensive nature of the variable speed motor.
In another conventional variable delivery pump adjustment of the flow rate is achieved by providing movable members which may be moved to adjust the clearance between the movable members and the fore ends of the impeller blades, as disclosed, for instance, in Japanese Laid-Open Pat. No. 79817/1986. However, in this pump he movable members which move relative to the impeller blades are disposed on an extension of the rotational shaft on which the impeller is mounted.